Biomimetic Materials for Engineering Stem Cells and Tissues - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 328

nanofi ber scaffolds or for modifi cation of electrospun nanofi ber matrix
surface with nanoparticles, as an attempt to mimic the native microenvi-
ronment of the tissue being repaired.

14.2.3 Phase Separation

Phase separation is a simple technique for the manufacture of nanofi ber
scaffolds, which involves various key processing steps such as polymer
dissolution followed by simultaneous phase separation and gelation.
Finally the solvent is removed and the scaffold is either freeze-dried or
the porogens are removed, resulting in porous scaffold as in Figure 14.2.
Taboas et al. have fabricated biomimetic scaffold with local and global
pores using solid free-form fabrication [19]. They have used an image-
based design (IBD) method to design the scaffold that mimics the external
shape and the internal porous architecture of the bone. They fabricated
8 mm diameter by 8mm height cylindrical molds with interconnected
pores. Polylactic acid (PLA) in chloroform was then cast into the mold
and solvent was evaporated under atmospheric pressure to create global
pores in the scaffold. For a local porous structure, the above process was
repeated with sodium chloride as the porogen. In a similar method of
fabrication by Hacker et al. , porous scaffolds with interconnected pores
were fabricated using particulate leaching with paraffi n microparticles as
the porogens [20]. The method involves the concomitant extraction of the
porogen and polymer precipitation in warm n-hexane. These reports, and
other studies, indicate that scaffolds that mimic the biological system in
terms of porosity can be fabricated using phase separation.

14.2.4 Self-Assembly

The process of self-assembly involves the spontaneous organization of
individual components to obtain an ordered structure. These individual
components are held by the synergistic interactions of weak noncovalent
forces like hydrogen bonding, ionic bonding, hydrophilic, hydrophobic

Solvent
extraction
& porogen
teaching

Porogen
dispersion

Phase
separation

Porous
scaffold

Polymer
solution

Figure 14.2 Schematic illustration of steps involved in phase separation.